by Jeff Zillgitt, USA TODAY Sports

by Jeff Zillgitt, USA TODAY Sports

Boston Celtics All-Star point guard Rajon Rondo has a torn anterior cruciate ligament in his right knee and will miss the rest of season, dealing the Celtics a serious blow to their playoff chances.

The injury was announced Sunday during the Celtics' home game against the Miami Heat. No date has been set for Rondo's surgery.

"Oh my God," Pierce told ABC's Doris Burke when she informed him of Rondo's injury after the Celtics defeated the Heat 100-98 in double overtime.

Pierce sounded and looked like he was hearing the news for the first time.

"We've just got to rally around each other," Pierce said. "I feel for him. He was having such a great season, making the All-Star team. It's disappointing news. Guys just have to step up."

Rondo was said to have hyperextended his right knee in Friday's 123-111 double-overtime loss at the Atlanta Hawks. Rondo played 45 minutes and recorded his second triple-double in a row.

Rondo, Boston's most important player, was a late scratch Sunday after gingerly working out before the game and left for New England Baptist for the MRI, which confirmed the injury. He told Burke that he was just bothered by soreness and never considered he had torn his ACL. The Celtics were concerned enough to send Rondo for the MRI.

Rondo's agent, Billy Duffy, said he expects Rondo to return to form just as Minnesota Vikings running back Adrian Peterson did from a similar injury â?? just as good and possibly even better than before the injury.

"Of course, until there's surgery, we don't know the gravity of it," Duffy told USA TODAY Sports. "But under any circumstance, I expect him, with his work ethic and body, to come back stronger than ever."

Rondo, who watched the final minutes of the Heat-Celtics game from courtside, is averaging 13.7 points, an NBA-high 11.1 assists and 5.6 rebounds in 38 games.

Celtics coach Doc Rivers received the news before the game but did not tell his players.

"Obviously, the Rondo news is tough. â?¦ Obviously, it was pretty emotional," Rivers told news reporters after the game. "We'll find someone who's ready in our locker room who will step up. You can write the obituary (on this season), but I'm not."

Rivers and Duffy are on the same page.

"We've got a guy in the NFL, Adrian Peterson, who we can look at," Rivers said. "Whatever he did, we'll do."

Boston's future becomes even murkier with the approach of the Feb. 21 NBA trade deadline. President of Basketball Operations Danny Ainge is not afraid of big trades but says he won't make one just for the sake of doing something. He previously has contemplated breaking up the team that began a run of excellence with Pierce, Kevin Garnett and Ray Allen in 2008.

The Celtics hold the East's final playoff spot; can they keep it without their most important player?

Garnett has a no-trade clause and has said he wants to retire as a Celtic. Pierce has no such clause and has a desirable contract â?? only $5 million of his $15.3 million deal is guaranteed for 2013-14. But Ainge might be not be ready to part with Pierce, who had a triple-double in Sunday's win.

It was the second double-overtime game in a row for the Celtics, who ended their six-game losing streak, the longest in the Garnett era.

Guard Courtney Lee started in Rondo's place but had just four points on 1-of-7 shooting. Heat forward LeBron James had 34 points, 16 rebounds and seven assists.

The Celtics began Sunday in eighth place in the Eastern Conference at 20-23. They had been just two games ahead of the Philadelphia 76ers and four games ahead of the Detroit Pistons. Could the Celtics be in the draft lottery year?

The Celtics have made the playoffs five consecutive seasons, winning the title in 2008, advancing to the Finals in 2010 and reaching the conference finals last season.

Without guard Ray Allen, who left in the offseason for the Heat, the Celtics have struggled as they added several players, including guard Jason Terry, Lee, forward Jeff Green (back after missing all of last season) and rookie big man Jared Sullinger.

Now that Rondo's injury impacts the rest of Boston's season, Celtics President of Basketball Operations Danny Ainge could make franchising-altering moves before the trade deadline expires Feb. 21.

Does this give Ainge more incentive to trade Pierce and end another strong era for the Celtics? Garnett has a no-trade clause in his contract. Ainge recently said he will not make a trade just for the sake of it, but Rondo's injury changes the dynamics.

The season-ending injury will prevent Rondo from playing in the All-Star game Feb. 17 in Houston. He was voted a starter for the Eastern Conference.

NBA Commissioner David Stern will select Rondo's replacement â?? possibly Brooklyn Nets center Brook Lopez, who was not selected by fans or the coaches. Either the Philadelphia 76ers' Jrue Holiday or Cleveland Cavaliers' Kyrie Irving likely will start in Rondo's place.